FIGS. 1 to 4 are cross-sectional views showing a related art stack-type flash device formed using a hard mask according to a related art.
Referring to FIG. 1, a device isolating pattern (not shown) and a tunnel oxide film 2 is formed on a semiconductor substrate 1. An auxiliary polysilicon pattern 3 to be used as a floating gate is formed on the tunnel oxide film 2.
Next, an oxide-nitride-oxide (ONO) film 4 is formed on the auxiliary polysilicon pattern 3, and a polysilicon layer 5 to be used as a control gate is formed on the ONO film 4.
Then, a hard mask layer 6 made of an oxide film or a nitride film is formed on the polysilicon layer 5.
An argon fluoride (ArF) photoresist pattern 7 is disposed on the hard mask layer 6.
The hard mask layer 6 is typically formed under the lower surface of the ArF photoresist pattern 7 since the ArF photoresist pattern 7 often has a thinner coating thickness than a krypton fluoride (KrF) photoresist pattern. This makes it difficult to form a stack gate thicker than the ArF photoresist pattern 7. Accordingly, the hard mask layer 6 is typically formed under the ArF photoresist pattern 7.
Referring to FIG. 2, the hard mask layer 6 can be patterned using the ArF photoresist pattern 7 as an etch mask to form a hard mask pattern 8 on the polysilicon layer 5 to be used as a control gate.
Next, referring to FIG. 3, the polysilicon layer 5, the ONO film 4, the auxiliary polysilicon pattern 3, and the tunnel oxide film 2 are etched using the hard mask pattern 8 as an etch mask. Accordingly, a flash device 10 comprising a tunnel oxide film pattern 2a, a floating gate 3a, an ONO pattern 4a and a control gate 5a is formed on the semiconductor substrate 1.
Referring to FIG. 4, after forming the flash device using the hard mask pattern 8, the hard mask pattern 8 is removed from the flash device 10.
The hard mask pattern 8 is typically removed by performing a wet etching process, such as a vapor phase chromatography (VPC) process. During the wet etching process, an oxide film pattern and a nitride film pattern in the exposed ONO pattern 3a of the flash device 10 are often damaged (see, e.g. 4b).
In the flash device 10, the ONO pattern 3a is very important in charging and discharging electrons. Thus, if the ONO pattern 3a is damaged, the capacity of the flash device 10 is largely degraded.
Thus, there exists a need in the art for an improved flash device and fabricating method thereof.